燃焼合成法によるＴｉＡｌ基金属間化合物粉の焼結組織と疾労特性

Abstract

Microstructure, fatigue properties, tensile strength, density and phase identification have been investigated for sintered compacts of TiAl base intermetallic compound powders prepared by combustion synthesis from pure titanium and aluminum powders. The results obtained are as follows: Both the TiAl powder prepared by the combustion synthesis and the compacts sintered at 1523-1648K for 25.2ks consist of γ-TiAl and α2-Ti3Al. The microstructure of the sintered compacts is dependent on the sintering temperature. The compacts sintered at 1523 and 1553K show equiaxed grains of the γ-and α2-single phase, and the compacts sintered at 1573 and 1648K contains α2/γ lamellar grains in addition to the γ-and α2-single phase grains. The amount of voids in the sintered compacts decreases with increasing sintering temperature and the relative density increases with increasing sintering temperature. The compact sintered at 1523K which contains most voids shows the lowest fatigue strength and the compact sintered at 1553K consisting of the (γ+α2) fine microduplex structure shows the highest fatigue strength. Preferential nucleation of cracks at theα2/γ lamellar interfaces in the compacts sintered at 1573 and 1648K brings about decrease in fatigue strength. The ratio of fatigue strength (at 107 cycles)to the tensile strength (UTS) is about 0.6 to 1.0, and decreases with increasing temperature. Large value of the fatigue ratio is characteristic of TiAl base intermetallic compounds.